A new functional device in which a CMOS circuit and a MEMS part are brought together will be achieved by the advancement of semiconductor processing technology and extension of micro-machining technology, so-called MEMS (Micro-Electro-Mechanical Systems) technology. For instance, it is thought that the switching function to switch a re-configurable logic device is carried out by using a MEMS switch.
A re-configurable logic device or a programmable logic device (PLD) is a flexible LSI in which a plurality of circuit configurations selectable by the user have been readied on a chip and operations, such as an addition function and a changing function, are achieved by freely switching the circuit configuration after the user has purchased a completed chip. There are merits on the user side, such as shortening the development time and cost reductions. When the machining size is decreased to 65 nm by improvements in semiconductor process technology, it is said that the market development of a PLD core will be accelerated more since problems of the area efficiency and cost can be solved even if generic logic is mounted on a chip. However, the problems of quality and power consumption of the entire chip still remain.
If the change of the circuit configuration of this re-configurable logic device can be achieved by a MEMS switch which is simultaneously formed with a circuit element by using a CMOS process, the problem of power consumption can be solved without a significant price increase. Since electrical signals in a MEMS switch are transmitted by the contacting of mechanical elements with each other which are composed of a metallic material, the parasitic resistance is small during an ON operation. Therefore, if it is simultaneously manufactured with a CMOS circuit element, it can be achieved by adding a few steps to the existing circuit process. However, on the other hand, in order to achieve the practical use of a MEMS switch, the problem still remains in the reliability of the contact terminal part which transmits the electrical signals.
A MEMS switch formed by using a conventional semiconductor process is like the one, in general, shown in FIG. 1 (for instance, refer to JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 11, NO. 2, APRIL 2002 147 “Integrated Microrelays: Concept and Initial Results” Han-Sheng Lee et al.). The MEMS switch shown in FIG. 1 moves a cantilever beam (cantilever contact arm) 101 by a pull-in electrode (driving mechanism) 102 and lets a fixed contact (fixed contact arm) 103 opposite the cantilever beam 101 physically contact the cantilever beam 101, resulting in the switch being opened and closed. Therefore, a low resistivity metal such as Au and Cu is used for a metallic material comprising the cantilever beam 101 and the fixed contact 103 and, for instance, they are fabricated by using a vacuum evaporation technique, plating technique, and a sputtering technique.
When such a MEMS switch is used in practice, there is a problem that metals comprising the contacts become welded to each other during the switching action of the switch. Concerning this problem, in JP-A No. 67964/2001, welding and dislocation are prevented without increasing the contact resistance by forming a high melting point metal with high hardness or a super-ultra thin film of an insulator at the contact terminal part of the switch, resulting in the avoidance of deterioration due to aging. In this technique, when the super-ultra thin film is an insulator, the signal is transmitted by a tunneling current flowing in the film.